"1 db minta a félhullám véletlenszerûen kiválasztott pontján"
Nem annyira véletlenszerû:
"B < 1/(2T) sávra határolt abszolút integrálható analóg jelek T közû mintáik"
Forrás: Géher Károly - Híradástechnika
"The continuous signal varies over time (or space as in a digitized image or another independent variable in some other application) and the sampling process is done by simply measuring the continuous signal's value every T units of time (or space), which is called the sampling interval. In practice, for signals that are a function of time, the sampling interval is typically quite small, on the order of milliseconds or microseconds or less. This results in a sequence of numbers, called samples, which is to represent the original signal. Each sample is associated to the specific point in time where it was measured. The reciprocal of the sampling interval, 1/T is the sampling frequency, fs, and measured in samples per unit time. If T is expressed in seconds then fs is expressed in Hz."
"The primary disadvantage of analog signaling is that any system has noise – i.e., random variation. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant. Electrically, these losses can be diminished by shielding, good connections, and several cable types such as coaxial or twisted pair.
The effects of noise make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise as well. Even if the resolution of an analog signal is higher than a comparable digital signal, in many cases, the difference is overshadowed by the noise in the signal."
Noise is any disturbance in an electrical current that is not part of the signal, and every current carries a certain amount of this electrical garbage.
Since an analog dupe is an imitation, it happily copies the noise right along with the parent signal, while adding new noise in the process. That means that in each generation, the noise level relative to the signal (signal-to-noise ratio) increases and the quality decreases proportionately.
In digital recording, noise is not a problem because the signal consists entirely of current pulses carrying information like Morse code: power on = 1; power off = 0. If the voltage level of the "power on" part of the signal is well above the noise level, then the transcribing (copying) system can be set to respond only to current at that level and ignore the noise entirely. So even if the process adds a small amount of its own noise, it never copies the parental noise--nor does it pass on its own noise to the grandchildren.
The result is that digital video can be copied through many generations without appreciable quality loss. This is a massive improvement over analog video (and even over cinematic film, which is another analog medium)."